This invention relates to an apparatus and method for forming cylindrical magnet assemblies for rotating electrical machines.
In many forms of rotating electrical machines, there is provided a cylindrical shell that contains a plurality of circumferentially spaced permanent magnets. Generally these magnets are retained within the shell by a magnet case that is complimentary to the shell. However, recently the use of high energy neodymium based magnets has replaced ferrite based magnets. By using these high energy neodymium based magnets, it is possible to increase the magnetic intensity while at the same time, reducing the size of the components. However, because of their high magnetic strength, it is necessary to insure that the magnets are rigidly held within the cylindrical shell.
One way it is proposed to maintain the magnets in position is to deform or fold the edge of the shell into engagement with the magnets so that they are trapped between two flanges thus formed on the shell. However, the previous methods for forming this have resulted in a cumbersome operation which has been difficult to obtain automatically and required two separate forming steps in different stations.
It is, therefore, a principle object to this invention to provide an improved and simplified apparatus and method for assembling the permanent magnets of a rotating electrical machine.
It is a further object to this invention to provide an improved method and apparatus for retaining the permanent magnets in position within a cylindrical shell, which is versatile and can be adapted for use with various sized shells.
A first feature of the invention is adapted to be embodied in a machine for folding over a peripheral flange of a cylindrical shell. The apparatus comprises a support for the shell, a forming tool having a pre-bending section and a final bending section angularly related to each other about a plane extending parallel to the support and a drive. The drive is effective to cause relative axial movement of the support and the forming tool to bring the forming tool into engagement with a peripheral flange of a shell positioned on the support. The drive also effects relative radial movement of the support and the forming tool for determining which of section of the forming tool engages the peripheral flange of the shell positioned on the support. In addition, the drive effects relative rotation of the support and the forming tool to deform a circumferential portion of the peripheral flange of the shell positioned on the support. A control operates the drive for first partially bending the peripheral flange of the shell positioned on the support around a circumferential area by the pre-bending section of the forming tool and then completes the bending thereof by the final bending section of the forming tool.
Another feature of the invention is embodied in a method of forming a magnet assembly for a rotating electrical machine. The method comprises the steps of forming a shell having a cylindrical section open at one end and at least partially closed at its other end by a radially extending end wall extending radially inwardly from the cylindrical section and an extending section thereof at the open end of said shell. A plurality of magnetic sections are placed within the shell with their outer periphery in engagement with the inner surface of the cylindrical section and one end thereof in engagement with the end wall. The extending section of the shell is initially bent toward the magnetic sections by bringing a first section of a forming tool into axial contact therewith and then continuing to bend a circumferential extent of the extending section by effecting relative rotation between the shell and the forming tool around the axis of the cylindrical section. Then the extending section is finally bent of into locking engagement with the magnetic sections by bringing a second section of the forming tool into contact with the extending section and effecting relative rotation between the shell and the forming tool around the axis of the cylindrical section.